Will Davis - Copyright 2010. Nuclear energy news, insight and analysis. Coverage of events world wide, including new plant construction, operation of plants now in service, and shutdown and decommissioning of plants. APR emphasizes the technology of nuclear energy, as well as the history of the development of that technology. Your #1 nuclear energy source!

APR: your source for nuclear news and analysis since April 16, 2010

Wednesday, May 4, 2011

TEPCO responds to NISA on reactor building, and more

Surprisingly, TEPCO has made a press release in the middle of the night (Tokyo time) to cover some of NISA's requests. It includes a rather complicated sixteen page handout which we'll summarize below.

-TEPCO is improving the conditions in the reactor building to allow for the performance, in the near term, of three jobs: First, installation of new water level measuring equipment for the pressure vessels; second, installation of the new external cooling facility; third, for the purpose of making new connections for the nitrogen feed to the containment vessel.

-TEPCO will recalibrate existing RPV and dry well level meters, and install new RPV measuring meters.

-Dry well flood level will be closely monitored so as not to flood the vent lines.

-TEPCO has finally revealed some details about the actual construction of the temporary cooling system it will install.. at least at Unit No. 1. Here is a clip from the handout:As stated on the handout, existing systems will be combined with new connections and new systems to provide cooling. Notable features here are as follows:

*Use of an air blast cooling tower*Use of heat exchanger internal to reactor building*Supply of water in primary circuit both to pressure vessel and dry well

-Nitrogen injection will be disrupted by the new design, but TEPCO already has another location to inject the required nitrogen into the dry well and work to connect temporarily to this will be concurrent with that performed on the temporary cooling system.

-General dose rates in the expected work area are about 10 mSv/hr (in the US we'd rate this as 1000 mR/hr.) The reduction to the required <1mSv/hr (or less than 100 mR/hr) will be accomplished through reduction of airborne activity, removal of contaminated debris, and installation of shielding.

-Filtration of the reactor building atmosphere will also include a plan using further Alara Venti units to pressurize the air lock and reactor building, ensuring no leakage of contaminated air to the environment.

-There will be about one hour of open access through the unpressurized air lock to implement work; external release and exposure will be very closely monitored during this time.

-TEPCO's preliminary time line through the end of installation of the final components to achieve the temporary core cooling, and all prior required functions, is shown below.Click photos on this page to enlarge.

1 comment:

Very interesting document and plan.The heart of the effort is apparently to flood the primary containment up to about the lower fuel level of the RPV, presumably cooling the RPV through the shell, while recirculating the primary containment water.Does this not specifically run against NISAs fear that a filled primary containment would be much more vulnerable to aftershocks?Also, this approach assumes the primary containment is intact. So while it may work here, TEPCO will need different approaches to reactors 2 and 3.Still, it offers promise to end the leakage of radioactive material from reactor 1, a good first step.